The present invention generally relates to alarm systems, and more specifically to an alarm system which includes one or more remote stations connected to a control station by only three leads but which nevertheless permits remote control of the alarm system and which provides numerous visual indications of the status of the alarm system at the central as well as remote locations.
There are numerous alarm systems, including intrusion as well as fire, already known. While the basic circuitry of such alarms is relatively simple, many of the known alarms incorporate means for increasing the effectiveness of the alarm system, decreasing the number of false alarms, minimizing power consumption or prevention of tampering with the system. Typical alarms of the aforementioned types are disclosed in U.S. Pat. Nos. 3,351,934; 3,641,552 and 3,828,340.
The use of remote stations which permit supervision of the alarm system are also known. With such an arrangement, there is typically provided a central control box which includes the bulk of the circuitry of the system as well as the power supplies and stand-by batteries for energizing the system. The control boxes are normally concealed and locked so that tampering therewith is not possible without actuating the alarm. When remote stations are provided, these are connected to the control box and permit limited control of the alarm system. Sometimes, the remote stations provide an indication of the status of the alarm system. U.S. patents which disclose alarm systems having remote stations are U.S. Pat. Nos. 3,174,143, and 3,747,093. The use of LEDs in alarm systems is also known and disclosed in U.S. Pat. No. 3,706,987.
As is well known to those skilled in the art, a major expense involved in the installation of alarm systems is the labor required to wire the electrically conductive leads or wires throughout the premises to be protected. When remote locations are utilized, these must clearly also be wired to the control box, and this involves additional time and expense. In this connection, an objective of numerous prior art alarm systems has been to connect the remote stations which cooperate with the central control box by the minimum number of leads while providing the maximum amount of control or supervision over the alarm system, as well as providing the maximum number of indications of the status of the alarm system. The invention to be described permits the use of only three leads to connect each remote station to the control station while providing four or five distinct visual indications of the status of the alarm system, as well as providing supervisory control over the system to permit the same to be enabled or disabled from any of the remote locations. The known alarm systems have not provided such extensive information concerning the status of the alarm system, as well as providing control of the system at the remote locations when the remote stations have been connected to the control station by only three leads or conductors.